Plastic-bonded explosive compositions and the preparation thereof

ABSTRACT

1. A PLASTIC-BONDED EXPLOSIVE COMPOSITION COMPRISING A HIGH EXPLOSIVE SELECTED FROM THE GROUP CONSISTING ESSENTIALLY OF DIAMINOTRINITROBENZENE, CYCLOTETRAMETHYLENENITRAMINE, AND MIXTURES THEREOF, THE COPOLYMER OF VINYLIDENE FLUORIDE AND PERFLUOROPROPENE AND A SYNTHETIC ORGANIC SILICON RESIN.

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The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to new and improved plastic-bonded explosive compositions and the preparation thereof. In one of its more specific aspects it relates to a novel binder system for plastic-bonded explosives.

In the field of compressible explosives it has been found that most of the high temperature binders, includinng fluorinated binders, with such conventional curing agents as benzoyl peroxide and organic amines require high curing temperatures in order to achieve desired physical properties. Pressed densities were often low initially, were further lowered by curing conditions, or costly modifications were required to permit curing under pressure.

The general purpose of this invention is to provide a suitable binder for an insensitive, heat resistant, plastic bonded, compressible explosive, which embraces all the advantages of similarly employed binder systems and possesses none of the aforedescribed disadvantages.

An object of the present invention is the provision of a compressible explosive composition to be used in applications involving aerodynamic heating.

Another object is to provide a plastic bonded explosive which has the economic advantages of savings in time and equipment in preparation.

A further object of the invention is the provision of a binder system for explosives which reduces possible safety hazards at high temperatures.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same become better understood by reference to the following detailed description.

Broadly, this invention contemplates incorporating a new binder for plastic-bonded explosives comprising a fiuorocarbon-silicone system which would, among other things, eliminate lengthy, high-temperature postcuring cycles previously considered necessary to obtaindesired physical properties. The optimum parent explosive composition comprises about 95% diaminotrinitrobenzene (hereinafter referred to as DATB), about 4% of a copolymer of vinylidene fluoride and perfluoropropene (hereinafter referred to as Viton) and 1% of a synthetic organic silicone resin (hereinafter referred to as Chemlok) This ratio of fluorocarbon to silicone gives the best physical properties consistent with good processability. Cyclotetramethylenetetranitramine (HMX) was substituted in place of diaminotrinitrobenzene (DATB) with good all-around results.

In the following examples of plastic bonded explosive compositions made in accordance with the present invention, it will be understood that they are exemplary and are not to be construed as limited the invention.

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Percent Ingredients composition Example 1:

DATB 95 Binder (Viton, 4%; Chemlok, 1%) 5 Example 2:

DATB 95 Binder (Viton, 2.5%; Chemlok, 2.5%)- 5 Example 3:

DATB 95 Binder (Viton, 4.5%; Chemlok, 0.5%) 5 Example 4:

DATB 95 Blnder (Viton, 3.5%; Chemlok, 1.5%) 5 Example 5:

DATB H MX 25 nder (Viton, 4%; Chemlok, 1%) 5 Example 6:

D 47. 5 HlvIX 47. 5 Binder (Viton, 4%; Chemlok 1% .5. 0 Example 7:

DATB 25 HMX 70 Binder (Viton, 4%; Chemlok, 1%). 5 Example 8:

HMX Al r 20 B nder (Viton, 4%; Chemlok, 1%) 5 Example 9:

HM 9. 9 Al 5. 0 Binder (Viton, 5%; Chemlok, 0.1%) 1 The binder ingredients of the above examples may vary from about 2.5 to 4.5% by weight Viton and from about 0.1 to 2.5% by Weight Chemlok.

All the DTAB-Viton-Chemlok formulations above set out were initially made in a Baker-Perkins mixer. The Chemlok, which is supplied in methanol solution, was first applied as a precoat to the DATB and the solvent was partially removed by evacuation. The Viton, dis.- solved in either acetone or ethyl acetate, was then incorporated. After thoroughly mixing, the material was dried under vacuum at ambient temperature.

For greater safety in processing, particularly where large batches were to be made, it was considered desir: able to devise a slurry procedure. Two were studied and both gave essentially the same type pressed product with the same characteristics as those resulting from the Baker-Perkins approach.

The processing methods used in preparing the plasticbonded explosive compositions of this invention will now be described.

EXAMPLE A Aqueous slurry method for preparing a DATB-Viton- Chemlok composition Components: Percent by weight DTAB Viton 4 Chemlok 1 tinued for about 45 minutes at approximately rpm.

until a smooth consistency resulted. 25 pounds of tap water were added under continued agitation, the mixing rate being reduced slightly and agitation continued for from 1 to 2 minutes. The water was then decanted and the resulting coagulant filtered, aspirated and oven dried at 80 C. Approximately 2267 grams of the DATB- Viton-Chemlock explosive resulted having the composition as h'ereinabove set forth.

It should be noted that the particle size of the final product may be affected by the rate of water addition. The optimum rate must be determined for each piece of equipment and for each size batch.

EXAMPLE B Aqueous slurry method for preparing HMX-DATB- Viton-Chemlok composition Components: Percent by weight HMX 70 DATB 25 Viton 4 Chemlok 1 EXAMPLE C Aqueous slurry method for preparing HMX- Al-Viton-Chemlok composition Components: Percent by weight HMX 75 Al 20 Viton 4 Chemlok 1 100 grams of the above composition (Example 8) were prepared as follows:

4 grams of Viton were dissolved in 80 m1. of ethyl acetate forming a Viton lacquer. 75 grams of HMX were placed in a mixing kettle to which the Viton lacquer, prepared beforehand, was added and hand-mixed. 20 grams of aluminum and 20 ml. of Chemlok (containing 1 gram of solids) were added and processed under the same conditions as described in Example A.

EXAMPLE D Non-aqueous slurry method for preparing DATB- Viton-Chemlok composition Components: Percent by weight DATB 95 Viton 4.2 Chemlok 0.8

20 grams of a plastic-bonded explosive having the above composition were prepared as follows:

0.84 gram of Viton was dissolved in 15 ml. of ethyl acetate. 19 grams of DATB were placed in the mixing kettle to which 80 ml. of ethyl acetate were added and then hand-mixed. 15 ml. of the Viton-ethyl acetate solution and 3.20 ml. of Chemlok in methanol (containing about .16 gram of solids) were now added and mixed until all lumps were broken down and the material appeared homogeneous. 150 ml. of Stoddard Solvent were added during continued agitation. (Hexane may be used in lieu of Stoddard Solvent.) The mixture was stirred very slowly for 2-3 minutes, then the liquid decanted and the product or coagulant filtered, aspirated, and oven dried at 80 C.

4 EXAMPLE E Baker-Perkins method for preparing DATB- Viton-Chemlok compositions Components: Percent by weight DATB 95 Viton 4 Chemlok 1 200 grams of a plastic-bonded explosive having the above composition (Example 1) were prepared by the following procedure:

8 grams of Viton were dissolved in 160 ml. of acetone by refluxing and stirring. 190 grams of DATB were weighed out and placed in a Baker-Perkins mixer. 40 ml. of Chemlow (containing 2 grams of solids) and the Viton-acetone solution were added along with additional acetone as may be required to maintain a fluid paste. The ingredients were mixed well at 30-40 r.p.m. When all lumps were broken down and the mixture appeared smooth and homogeneous, vacuum was applied with continued mixing to remove acetone. When most, but not all the solvent was removed, the damp material was transferred to trays and dried in an oven at C.

In the studies which led to the present invention a number of dilferent binder mixtures comprising Viton and Chemlok were evaluated, with respective ratios of Chemlok and Viton ranging from 50-50 down to 5-95. The higher Chemlok concentrations produced a strong but brittle pressed composition, which showed a tendency to crack upon exposure to thermal shock. Also under certain pressing conditions high pressed densities were more diflicult to achieve when the Chemlok content exceeded 20% of the total binder. The optimum percentage of Chemlok in the binder appears to be about 0.8 to 1.0% of the total composition. This concentration was found to be most consistent with good compressibility, high initial strength, and retention of strength after exposure to heat.

The Chemlok percentages are based on the commonly supplied methanol solution which runs about 5 percent solids by evaporation. This material tends to be basic in nature.

Table I below shows some properties of a typical optimum composition containing nominally parts DATB, 4 parts Viton and 1 part Chemlok. One-half-inch diameter cylinders were pressed at 135 C., 20,000 p.s.i. and 5 minutes dwell, with die cooling before ejection. Ten samples were tested for compressive strength and modulus. Detonation velocity was determined in triplicate.

TABLE I Properties of DATB-Viton-Chemlok compositions Impact sensitivity No fires at 300 cm Autoignition point, C2 275-285, DATB melts. Vacuum thermal stability, ml./

g./48 hr.:

at C. 0.2.

at 200 C. 3.0. Detonation velocity, m./sec. 7295 at 98.3% TMD. Plate dent, inches 0.09.

Compressive strength, p.s.i. 14,300.

2.5 kfl. wt., type 12 tool, 35 mg., li -ln. D Pellets. Composltion B std. 50% pt.=3739 cm.

2 2 C./min. temperature rise. Samples inserted in steel block. Recorded temperature is that of block at time transition OCCUI'S.

Measured for /2'11'1- D x %-in. high pellets pressed at 9., 5 min. dwell, 20,000 p.s.i., and ejected at ambient temperaure.

Table 11 following presents physical strength data at various temperatures for compositions containing varying amounts of synthetic organic silicone (Chemlok 607) in the binder. Ten samples were pressed, each at 135 0., 20,000 p.s.i., and 5 minute dwell with cold ejection. All samples were held at the test temperature for a minimum of two hours prior to testing.

TABLE II [95% DATE, 5% Viton-Chemlok binder] Test Compr Percent Chemlok total temp., Compr. SD, modulu composition F. p.s.i. p.s.i. p s.i. 10

N'1E.A1l samples in. D x in. high, pressed at 130140 0., 20,000 p.s.i., fi-minute dwell, ejection at ambient temperature. Density range 98.499.0% TMD. Molding powder prepared by Baker-Perkins techmque.

Substitution of HMX for some of the DATB in DATB- fluorocarbonsilicone compositions appears to be a feasible means of increasing energy potential without necessitating too great a sacrifice in sensitivity.

Autoignition values for various DATB-HMX-Viton- Chemlok compositions are presented in Table III below.

TABLE III Autiognition values for HMX-DATB-Vitron-Chemlok compositions [Heating rate2 O./min.]

Endothermic Ignition auto- Composition DATB-HMX-Vitontransiexotherm, ignition Chemlok tions, 0. 0 point, C.

ATB- 277 294 301 HMX-Chemlok 95/5 183 216-219 238440 HMX-Viton, 95 5 192-195 253-255 259-263 DAIB alone 280-282 291 295-296 HMX alone 8 (98% min. purity) 196 250 2 e No Chemlok in composition.

b No Viton in composition, compatibility, test.

0 Same batch as that used in formulations.

5 None observed.

e V. sudden ign.

Values for the pure explosive, i.e., without binders, and for a. few binary compositions are also shown for comparison. The variation in reproducibility of these temperatures may range as high as :5" C.; however, it is usually within 2-3 C.

Examination of the autoignition results shows the immediate etfect of HMX substitution to be a lowering of the ignition point to a value slightly but significantly below that of HMX by itself. This efiect is observable even when comparatively small percentages of HMX are present (10%). The reduction below 255 C., the autoignition point of HMX alone, is probably due to some interaction between the HMX and Chemlok and possibly to a lesser extent between DATB and HMX, since compositions in which these combinations occur seem to ignite consistently at a temperature lower than that for HMX alone. Another noteworthy observation is the rapadity with which the ignition of the HMX-DATB- Viton-Chemlok compositions occurs once the final exotherm is initiated. This phenomenon does not appear to be characteristic of the binary mixtures containing either one or the other explosive constituent plus Chemlok or Viton.

The physical properties of DATB-HMX-Viton-Chem- 10k compositions are illustrated in Table IV following:

TABLE IV The effect of composition on compressibility and physical properties of HMX-DATB-Viton-Chemlok, 5% total binder a Compressive Avg. compressibility strength HMX-DAB'I, Density, TMD, Range, MEX10-, percent g./cm. percent P.s.i. b p.s.i. p.s.i.

B Nominal binder composition was 4 parts Viton A-HV to 1 part Chemlok 607 unless noted otherwise.

b Two-hour minimum preheat at (3., 20,000 p.s.i., 0., 4 mm. or less vacuum, 20 min. dwell, hot ejection.

0 Binder composition was 4.2 parts Viton to 0.8 parts Chemlok.

It is noted that as the HMX content increases, mechanical strength falls off markedly. This observation has been confirmed in similar investigations on analogous aluminized systems. HMX-Viton compositions in general do not seem to yield as high compressive strength values as DATE-Viton or HMX-nylon. The inclusion of additional Chemlok in the binder as set out in this invention do doubt improves the properties of formulations high in HMX.

The DATB-Viton-Chemlok compositions, herein disclosed, after pressing are very resistant to attack by solvents such as ethyl acetate. This possibly indicates some kind of crosslinking action since DATB-Viton alone has no solvent resistance. When 'HMX is included in the DATB-Viton-Chemlok formulation, solvent resistance dropped somewhat. It was still superior, however, to the DATE-Viton without Chemlok.

The effect of 300 F. exposure on pellets pressed from the various compositions is shown in Table V below. Each entry represents an average of two determinations except the zero time results which were taken from Table IV. Again, the overall decrease in compressive strength with increase in HMX content may be noted. Furthermore, the samples which contained HMX appear to deteriorate to a somewhat greater extent in respect to compressive strength. Temperature effects on dimensions and density did not appear to vary much as HMX increased.

TABLE V The eflect of high temperatures on the physical properties of various HMXDATB-Viton-Ohemlok compositions (%-in. D pressed cylinders exposed to 300 F. 11 5% total binder, 4:1 Viton-Chemlok) Percent linear dimen- Density Final HMX-DATE, Hours sional los compr. Decrease, percent exposed increase b percent str. percent 1 0. 4 0. 8 11, 200 4. 3 3 0. 7 0. 9 11, 500 1. 7 24 0. 7 1. 1 11, 700 None Pressing conditions: 2hr. min. preheat; 20,000 p.s.i.; 125 0.; 4 mm.

vacuum; 20min. dwell.

b All observable change was in height. Diameters remain constant:

Substitution of HMX for some of the DATB in DATB- fiuorocarbonsilicone compositions as herein disclosed appears to be a feasible means of increasing energy potential without necessitating too great a sacrifice in sensitivity. Resulting impact sensitivity varies with percentage of HMX. Resulting autoignition values for all hybrid compositions approximate those of HMX by itself. This involves a drop of about 40-50 C. below the temperature at which DATB alone or with inert binders starts to melt. and ignite under comparable test conditions.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A plastic-bonded explosive composition comprising a high explosive selected from the group consisting essentially of diaminotrinitrobenzene', cyclotetramethylenenitramine, and mixtures thereof, the copolymer of vinylidene fluoride and perfluoropropene and a synthetic organic silicone resin.

2. A plastic-bonded explosive composition comprising diaminotrinitrobenzene, a copolymer of vinylidene fluoride and perfluoropropene and an organic silicone resin.

3. A plastic-bonded explosive composition comprising a mixture of cyclotetramethylenetetranitramine and diaminotrinitrobenzene, a copolymer of vinylidene fluoride and perfluoropropene and an organic silicone resin.

4. A plastic-bonded explosive composition comprising cyclotetramethylenetetranitramine, a copolymer of vinylidene fluoride and perfluoropropene and an organic silicone resin.

5. A plastic-bonded explosive composition comprising about 95% diaminotrinitrobenzene, about 4% copolymer of vinylidene fluoride and perfluoropropene and about 1% organic silicone resin.

6. A plastic-bonded explosive composition consisting essentially of about 95% by weight diaminotrinitrobenzene, from 2.5 to 4.5% by weight of the copolymer of 8 vinylidene fluoride and perfluoropropene and from about 0.5 to 2.5% by weight organic silicone resin.

7. Apro'cess forthe preparation of an improved plastic-bonded explosive comprising adding an acetone solution ofa copolymer of vinylidene fluoride and perfluoropropene to a weighed amount of diaminotrinitrobenzene and mixing for about 30 minutes until a homogeneous mixture results then adding a methanol solution of synthetic organic silicone and mixing again until the mixture has the consistency of paste, continuing mixing while adding a volume of water equal to about 6 times the volume of mixture, decanting excess liquid and drying the resulting residue overnight at C.

8. A process for the preparation of an improved plastic bonded explosive comprising adding an ethyl acetate solution of the copolymer of vinylidene fluoride and perfluoropropene and a methanol solution of the synthetic organic silicone resin to a weighed amount of diarninotrinitrobenzene and hand-mixing until a homogeneous mixture results, then adding hexane during continued agitation, until a coagulant forms, decanting the hexan filtering the coagulant and drying at 80 C.

References Cited UNITED STATES PATENTS 2,777,783 1/1957 Welch 260-42 B 2,865,795 12/ 195 8 Morrison 260-42 13 BENJAMIN R. PADGETT, Primary Examiner US. Cl. X.R. 14988, 92, 

1. A PLASTIC-BONDED EXPLOSIVE COMPOSITION COMPRISING A HIGH EXPLOSIVE SELECTED FROM THE GROUP CONSISTING ESSENTIALLY OF DIAMINOTRINITROBENZENE, CYCLOTETRAMETHYLENENITRAMINE, AND MIXTURES THEREOF, THE COPOLYMER OF VINYLIDENE FLUORIDE AND PERFLUOROPROPENE AND A SYNTHETIC ORGANIC SILICON RESIN. 